Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.     

Growth of crystalline quartz films with AT-cut plane by means of catalyst-enhanced vapor-phase epitaxy under atmospheric pressure

Crystalline quartz films with an AT-cut plane have been grown by catalyst-enhanced vapor-phase epitaxy, at atmospheric pressure, using two quartz buffer layers on a sapphire (110) substrate. In this method, the first quartz buffer layer was deposited on the sapphire (110) substrate at 773 K. After annealing at 823 K, the second buffer layer was deposited at 723 K. The crystal quartz epitaxial layer was then grown at 843 K. The X-ray full-width-at-half-maximum (FWHM) value of the crystalline quartz film obtained was smaller than that of crystalline quartz prepared using a hydrothermal process. The crystalline quality of the quartz films was dependent on the thickness of the buffer layers. Furthermore, it was found that angle control of the cut plane depended on the film thickness of the second buffer layer. The quartz films grown by vapor phase epitaxy show good oscillation characteristics at room temperature.     

Structural investigations of ITO-ZnO films grown by the combinatorial pulsed laser deposition technique

Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15 mm apart. The films were deposited on (1 0 0)Si and quartz substrates that were heated at temperatures from 300 to 500 °C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture.     

Room temperature weak ferromagnetism and magnetoconductance in functional CuO film

The granular CuO films are deposited on n-Si (1 0 0) and sapphire substrates using sol-gel route. Small microstrain leads to ∼5 times larger grain sizes (200-300 nm) and ∼2.5 times larger film thickness (∼0.57 μm) for sapphire than n-Si substrate, which are confirmed by X-ray diffraction and Atomic Force Microscopy. A diode-like current-voltage characteristics are observed for film deposited on n-Si substrate, which is absent for sapphire substrate. Typical manifestation of ferromagnetic character is observed for CuO films, which are strongly influenced by the substrates. Magnetic anisotropy is larger for sapphire substrate than n-Si substrate. At room temperature considerably large magnetoconductance ∼21% and soft ferromagnetic character of CuO film on n-Si substrate are attractive for functional applications.     

Characteristics of Ni films deposited on SiO2/Si(1 0 0) and MgO(0 0 1) by direct current magnetron sputtering system with the oblique target

280 nm-thick Ni films were deposited on SiO₂/Si(1 0 0) and MgO(0 0 1) substrates at 300 K, 513 K and 663 K by a direct current magnetron sputtering system with the oblique target. The films deposited at 300 K mainly have a [1 1 0] crystalline orientation in the film growth direction. The [1 1 0]-orientation weakens and the [1 1 1]- and [1 0 0]-orientations enhance with increasing deposition temperature. The lattice constant of the Ni films is smaller than that of the Ni bulk, except for the film grown on MgO(0 0 1) at 663 K. Furthermore, as the deposition temperature increases, the lattice constant of the films grown on the SiO₂/Si(1 0 0) decreases whereas that of the films grown on the MgO(0 0 1) increases. The films deposited at 300 K and 513 K grow with columnar grains perpendicular to the substrate. For the films deposited at 663 K, however, the columnar grain structure is destroyed, i.e., an about 50 nm-thick layer consisting of granular grains is formed at the interface between the film and the substrate and then large grains grow on the layer. The Ni films deposited at 300 K consist of thin columnar grains and have many voids at the grain boundaries. The grains become thick and the voids decrease with increasing deposition temperature. The resistivity of the film decreases and the saturation magnetization increases with increasing deposition temperature.     

Effects of crystalline quality on the ultraviolet emission and electrical properties of the ZnO films deposited by magnetron sputtering

The ZnO films were deposited on c-plane sapphire, Si (0 0 1) and MgAl₂O₄ (1 1 1) substrates in pure Ar ambient at different substrate temperatures ranging from 400 to 750 °C by radio frequency magnetron sputtering. X-ray diffraction, photoluminescence and Hall measurements were used to evaluate the growth temperature and the substrate effects on the properties of ZnO films. The results show that the crystalline quality of the ZnO films improves with increasing the temperature up to 600 °C, the crystallinity of the films is degraded as the growth temperature increasing further, and the ZnO film with the best crystalline quality is obtained on sapphire at 600 °C. The intensity of the photoluminescence and the electrical properties strongly depend on the crystalline quality of the ZnO films. The ZnO films with the better crystallinity have the stronger ultraviolet emission, the higher mobility and the lower residual carrier concentration. The effects of crystallinity on light emission and electrical properties, and the possible origin of the n-type conductivity of the undoped ZnO films are also discussed.     

Role of crystal orientation on the magnetic properties of CoFe2O4 thin films grown on Si (1 0 0) and Al2O3 (0 0 0 1) substrates using pulsed laser deposition

We report the influence of crystal orientation on the magnetic properties of CoFe₂O₄ (CFO) thin films grown on single crystal Si (1 0 0) and c-cut sapphire (Al₂O₃) (0 0 0 1) substrates using pulsed laser deposition technique. The thickness was varied from 200 to 50 nm for CFO films grown on Si substrates, while it was fixed at 200 nm for CFO films grown on Al₂O₃ substrates. We observed that the 200 and 100 nm thick CFO-Si films grew in both (1 1 1) and (3 1 1) directions and displayed out-of-plane anisotropy, whereas the 50 nm thick CFO-Si film showed only an (1 1 1) orientation and an in-plane anisotropy. The 200 nm thick CFO film grown on an Al₂O₃ substrate was also found to show a complete (1 1 1) orientation and a strong in-plane anisotropy. These observations pointed to a definite relation between the crystalline orientation and the observed magnetic anisotropy in the CFO thin films.     

Effects of sapphire substrate annealing on ZnO epitaxial films grown by MOCVD

The annealing effects of sapphire substrate on the quality of epitaxial ZnO films grown by metalorganic chemical vapor deposition (MOCVD) were studied. The atomic steps formed on (0 0 0 1) sapphire (α-Al₂O₃) substrate surface by annealing at high temperature was analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the ZnO films were examined by X-ray diffraction (XRD), AFM and photoluminescence (PL) measurements. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate surface. The optimum annealing temperature of sapphire substrates is given.     

Investigation of induced parallel magnetic anisotropy at low deposition temperature in Ba-hexaferrites thin films

In this paper we present the effect of low substrate temperature on structural, morphological, magnetic and optical properties of Ba-hexaferrite thin films. Films were deposited on single crystal Silicon (1 0 0) substrate employing the Pulsed Laser Deposition (PLD) technique. The structural, morphological, magnetic and optical properties are found to be strongly dependent on substrate temperature. The low substrate temperatures (room temperature to 200 °C) restrict the formation of larger grains. For the higher substrate temperature i.e., 400 °C, the grain size of the deposited thin film are much larger. The film grown at low substrate temperature do not show any anisotropy. As the substrate temperature is increased, the easy axis of the films alinged itself in the direction parallel to the film plane whereas the hard axis remained in the perpendicular direction. The higher substrate temperature caused the uniaxial magnetic anisotropy, which is very important in magnetic recording devices. The saturation magnetization and optical band gap energy values of 62 emu/cc and 1.75 eV, respectively, were achieved for the film of thickness 500 nm deposited at 400 °C. Higher values of coercivity, squareness and films thickness are associated with the growth of larger grains at higher substrate temperature.     

Crystallographic and magnetic properties of SrM thin films on Pt underlayer prepared at various substrate temperatures

Strontium ferrite (SrM) thin films deposited on thermally oxidized silicon wafer (SiO₂/Si) and single crystal sapphire with (0 0 l) orientation (Al₂O₃(0 0 l)) substrate using Pt underlayer were prepared by DC magnetron sputtering system. It was found that the intensity of (1 1 1) line for Pt and that of (0 0 l) diffraction line for SrM increases with increasing substrate temperature, T_u. The c-axis dispersion angle, Δθ₅₀, of SrM(0 0 8) depends on that of Pt underlayer. Both dispersion angle of Pt(1 1 1) and SrM(0 0 8) decrease with increasing temperature. It was observed that the saturation magnetization of SrM/Pt deposited on SiO₂/Si is higher than that of Al₂O₃ substrate. The coercivity and remanent squareness ratio in perpendicular direction are higher than that in in-plane direction. The maximum of coercivity in perpendicular direction of SrM/Pt films deposited on single crystal Al₂O₃ is about 4.2 kOe.     

Influence of Si substrate preparation on surface chemistry and morphology of L-CVD SnO2 thin films studied by XPS and AFM

Results of experimental studies of the influence of substrate preparation on the surface chemistry and surface morphology of the laser-assisted chemical vapour deposition (L-CVD) SnO₂ thin films are presented in this paper. The native Si(1 0 0) substrate cleaned by UHV thermal annealing (TA) as well as thermally oxidized Si(1 0 0) substrate cleaned by ion bombardment (IBA) have been used as the substrates. X-ray photoemission spectroscopy (XPS) has been used for the control of surface chemistry of the substrates as well as of deposited films. Atomic force microscopy (AFM) has been used to control the surface morphology of the L-CVD SnO₂ thin films deposited on differently prepared substrates. Our XPS shows that the L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit the same stoichiometry, i.e. ratio [O]/[Sn] = 1.30 as that of the layers deposited on Si(1 0 0) substrate previously cleaned by UHV prolonged heating. AFM shows that L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit evidently increasing rough surface topography with respect to roughness, grain size range and maximum grain height as the L-CVD SnO₂ thin films deposited on atomically clean Si substrate at the same surface chemistry (nonstoichiometry) reflect the higher substrate roughness after cleaning with ion bombardment.     

Photosensitivity of nanocrystalline ZnO films grown by PLD

We have studied the properties of ZnO thin films grown by laser ablation of ZnO targets on (0 0 0 1) sapphire (Al₂O₃), under substrate temperatures around 400 °C. The films were characterized by different methods including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). XPS analysis revealed that the films are oxygen deficient, and XRD analysis with θ-2θ scans and rocking curves indicate that the ZnO thin films are highly c-axis oriented. All the films are ultraviolet (UV) sensitive. Sensitivity is maximum for the films deposited at lower temperature. The films deposited at higher temperatures show crystallite sizes of typically 500 nm, a high dark current and minimum photoresponse. In all films we observe persistent photoconductivity decay. More densely packed crystallites and a faster decay in photocurrent is observed for films deposited at lower temperature.     

Effect of deposition temperature on the microstructure and surface morphology of c-axis oriented AlN films deposited on sapphire substrate by RF reactive magnetron sputtering

In this paper, c-axis oriented AlN films were prepared on sapphire substrate by RF reactive magnetron sputtering at various deposition temperatures (30–700 °C). The influences of deposition temperature on the chemical composition, crystalline structure and surface morphology of the AlN films were systematically investigated. The as-deposited films were characterized by X-ray photoelectron spectroscopy (XPS), two-dimensional X-ray diffraction (2D-XRD) and atomic force microscopy (AFM). The experimental results show that it can be successfully grown for high-purity and near-stoichiometric (Al/N = 1.12:1) AlN films except for the segregation of a few oxygen impurities exist in the form of Al–O bonding. The chemical composition of as-deposited films is almost independent of substrate temperature in the range of 30–700 °C. However, the crystalline structure and surface morphology of the deposited AlN films are strongly influenced by the deposition temperature. The optimum deposition temperature is 300 °C, giving a good compromise between crystalline structure and surface morphology to grow AlN films.     

Chemical composition of ZrC thin films grown by pulsed laser deposition

ZrC films were grown on (1 0 0) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40 Hz. The nominal substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that films deposited under residual vacuum or under 2 × 10⁻³ Pa of CH₄ atmosphere were crystalline, exhibiting a (2 0 0)-axis texture, while those deposited under 2 × 10⁻² Pa of CH₄ atmosphere were found to be equiaxed and with smaller grain size. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed the usual high oxygen contamination of carbides. Once the topmost 2-4 nm region was removed, the oxygen concentration rapidly decreased, down to around 3-8% only in bulk. Simulations of the X-ray reflectivity (XRR) curves indicated a smooth surface morphology, with roughness values below 1 nm (rms) and films density values of around 6.30-6.45 g/cm³, very close to the bulk density. The growth rate, estimated from thickness measurements by XRR was around 8.25 nm/min. Nanoindentation results showed for the best quality ZrC films a hardness of 27.6 GPa and a reduced modulus of 228 GPa.     

Anatase TiO2 films based CO gas sensor: Film thickness, substrate and temperature effects

Electrical response of anatase TiO₂ films is discussed for different concentrations of CO gas (20-100 ppm) in a nitrogen gas ambient. We investigated temperature (100-300 °C) and film thickness (100-1000 nm) effects for films deposited on glass, sapphire (0 0 0 1) and, Si(1 0 0) substrates. In general, there is a drop in resistance of the device when exposed to CO gas. Films deposited on sapphire showed a larger decrease in the resistance at 300 °C compared to those deposited on glass and silicon substrates. However, films grown on glass and silicon substrates showed a larger decrease in the resistance values for temperature around 200 °C when CO (ppm) values are greater than 40. The change in resistance of the films varies as square root of the CO gas concentration at 200 °C for films deposited on all the three substrates. In general, the decrease in resistance for thicker films is large compared to thinner ones, indicating participation of the bulk in the detection of CO gas. In the presence of O₂, film loses its sensitivity to CO gas when the concentration level of O₂ approaches 1800 ppm.     

Influence of substrate temperature on the texture of barium ferrite film by magnetron sputtering

Barium ferrite thin films have been prepared by radio frequency magnetron sputtering on a sapphire (0 0 1) substrate at substrate temperature of 500 °C and 650 °C, respectively. The films were further annealed in air at 1000 °C for 5 h. X-ray diffraction shows that the films at the lower substrate temperatures have a good epitaxial relation with respect to the substrate, while the samples under the higher substrate temperatures have (1 0 9) planes parallel to the substrate. The remanence ratio decreases from 0.82 to 0.47 when the substrate temperature is increased. We attribute the variation of the growth direction to the enhanced vertical mobility of the deposited atoms when the substrate temperature is increased.     

GaN films deposited by middle-frequency magnetron sputtering

GaN films were deposited on Si (111) substrates by middle-frequency magnetron sputtering. X-ray diffraction revealed preferential GaN (0 0 0 2) orientation normal to the substrate surface for all the films deposited. The diffraction intensity and N contents were found to depend strongly on the total gas pressure. Good quality films were only obtained at pressures in the range of 0.4-1.0 Pa. Little diffraction of GaN (0 0 0 2) could be observed either at total pressures below 0.4 Pa or above 1.0 Pa. The GaN films produced under the optimized conditions have an N:Ga ratio of 1:1 as determined by energy-dispersive X-ray spectroscopy.     

Effect of annealing on thermal stability and morphology of pulsed laser deposited Ir thin films

Iridium (Ir) thin films, deposited on Si (1 0 0) substrate by pulsed laser deposition (PLD) technique using Ir target in a vacuum atmosphere, were annealed in air ambient and the thermal stability was investigated. The crystal structure and surface morphology of Ir thin films before and after being annealed were studied by X-ray diffraction, Raman scattering, scanning electron microscope, and atomic force microscopy. The results showed that single-phase Ir thin films with (1 1 1) preferred orientation could be deposited on Si (1 0 0) substrate at 300 °C and it remained stable below 600 °C, which showed a promising bottom electrode of integrated ferroelectric capacitors. Ir thin films got oxidized to IrO₂ at temperatures from 650 to 800 °C.     

Influence of substrate crystallography on the room temperature synthesis of AlN thin films by reactive sputtering

A pulsed DC reactive ion beam sputtering system has been used to synthesize aluminium nitride (AlN) thin films at room temperature by reactive sputtering. After systematic study of the processing variables, high-quality polycrystalline films with preferred c-axis orientation have been grown successfully on silicon and Au/Si substrates with an Al target under a N₂/(N₂ + Ar) gas flow ratio of 55%, 2 mTorr processing pressure and keeping the temperature of the substrate holder at room temperature. The crystalline quality of the AlN layer as well as the influence of the substrate crystallography on the AlN orientation has been characterized by high-resolution X-ray diffraction (HR-XRD). Best ω-FWHM (Full Width at Half Maximum) values of the (0 0 0 2) reflection rocking curve in the 1 μm thick AlN layers are 1.3°. Atomic Force Microscopy (AFM) measurements have been used to study the surface morphology of the AlN layer and Transmission Electron Microscopy (TEM) measurements to investigate the AlN/substrate interaction. AlN grew off-axis from the Si substrate but on-axis to the surface normal. When the AlN thin film is deposited on top of an Au layer, it grows along the [0 0 0 1] direction but showing a two-domain structure with two in-plane orientations rotated 30° between them.     

Influence of target substrate distance on the properties of transparent conductive Si doped ZnO thin films

Si doped zinc oxide (SZO, Si3%) thin films are grown at room temperature on glass substrates under argon atmosphere, using direct current magnetron sputtering. The influence of the target substrate distances on structure, morphology, optical and electrical properties of SZO thin films is investigated. Experimental results show that the target substrate distances have a significance impact on the growth rate, crystal quality and electrical properties of the films, and have little impact on the optical properties of the films. SZO thin film samples grown on glasses are polycrystalline with a hexagonal wurtzite structure and have a preferred orientation along the c-axis perpendicular to the substrate. When the target substrate distance decreases from 76 to 60 mm, the degree of crystallization of the films increased, the grain size increases, and the resistivity of films decreases. However, when the distance continuously decreases from 60 to 44 mm, the degree of crystallization of the films decreased, the grain size decreases, and the resistivity of the films increases. SZO(3%) thin films deposited at a target substrate distance of 60 mm show the lowest resistivity of 5.53 × 10⁻⁴ Ω cm, a high average transmission of 94.47% in the visible range, and maximum band gap of 3.45 eV under 5 Pa of argon at sputtering power of 75 W for sputtering time of 20 min.